1. Field of the Invention
The present invention relates to a control circuit for charging and discharging, an illuminating apparatus and a driving method thereof, which control charging and discharging in an illuminating apparatus with a display portion composed of driven elements such as liquid crystal display or a plurality of light-emitting elements and so on.
2. Discussion of the Related Art
Recently, more than 1000 mcd of high-luminance light-emitting diodes have been developed for each of RGB, and production of large-scale LED display is started. The LED displays have characteristics that they can be lightweight and thinned, and they consume less power, etc. Hence, a demand for the LED displays as large-scale displays that can be used outdoors has been sharply increasing.
Practically, the large-scale LED display is composed of a plurality of LED units, which are combined corresponding to an installed location. The LED unit is composed of RGB of light-emitting diodes arranged in a dot matrix on a circuit board.
In addition, a driving circuit capable of driving each light-emitting diode individually is provided for the LED display. Concretely, LED-controlling devices transferring display data for respective LED units are connected in the LED display. A plurality of them is connected, and composes one large-scale display. In the case of a large-scale LED display, the number of the used LED units is increased, and one LED display is composed of, for example, a total of 120,000 LED units in 300×400.
Additionally, the dynamic driving method is used as a driving method of LED display. A concrete example is connected and driven as follows.
For example, in the case of an LED unit composed of m rows and n columns of a dot matrix, anode terminals of the light-emitting diodes (LEDs) arranged in each row are commonly connected to one of common source lines, and cathode terminals of the light-emitting diodes (LEDs) arranged in each column are commonly connected to one of current lines.
Then, m rows of common lines are switched ON successively at a predetermined period for displaying. In addition, a decoder circuit switches the m rows of common lines based on an address signal, for example.
Although an LED display apparatus using light-emitting diodes is explained above, the similar driving circuit (method) can also drive an electroluminescence display apparatus, a field emission type display apparatus (FED), or a liquid crystal display or the like.
However, there is a problem that electric charge remains in light-emitting diodes (light-emitting elements) connected to the common source line, which is not selected, or light-off status, while the light-emitting diodes (light-emitting elements), which are connected to the selected common source line, emit. Such a residual charge, which remains in the unselected period, produces an undesirable current when the common source line is selected. Such produced undesirable current reduces display quality because of undesirable-emission that the light-emitting diode, which is controlled not emitting, slightly emits, and insufficient contrast in display image. Accordingly, as shown in FIG. 3, a method of discharging the charge, which remains in the anode terminal of light-emitting diode connected to the unselected common source line, to ground by a circuit 37 composed of only resistor (R1) in the driving circuit is used. While, even using the circuit 37, if the light-emitting diode does not have enough rectification function, the undesirable current is produced in the other unselected common source line along a path shown by the arrow in FIG. 3. Therefore, the circuit cannot prevent the undesirable-emission that the light-emitting diode, which is controlled not emitting, slightly emits. The undesirable current caused by the residual charge etc. reduces display quality. Such a residual charge is produced not only in light-emitting elements but also in driven elements with a parasitic capacitance, which is driven in a driving-on status or a driving-off status. For example, there is the same problem in voltage control elements in a liquid crystal display. Additionally, this residual charge is produced not only in elements themselves but also in traces etc. connected to the elements as stray capacitances. Especially, in a large-scale display with long traces or numbers of traces, there is a problem such as an undesirable emission, false displaying, and false driving.
It is an object of the present invention to provide a control circuit for charging and discharging, an illuminating apparatus and a driving method thereof, which can reduce an influence of the above residential charge and can obtain a high-quality display such as an LED display, a liquid crystal display, an EL display, and a photoreceptor apparatus such as a CCD.